The present invention relates to a source-antenna for transmitting/receiving electromagnetic waves, more particularly a system of source-antennas allowing the reception of satellite television signals in a certain frequency band such as the Ku band lying between 10.7 and 12.75 GHz and of satellite communications in a second frequency band such as the Ka band at around 30 GHz in transmission and at around 20 GHz in reception, using just a single structure of antennas.
There are at present source-antenna structures for transmitting/receiving electromagnetic waves which operate with two frequency bands. These source-antennas make it possible to meet the requirements of satellite communication systems in respect of high bit rate multimedia applications. An antenna of this type has been proposed in patent WO 99/35111 in the name of THOMSON multimedia. These dual-band antenna structures are composed of two cofocused antennas. Thus, as described in the abovementioned patent application, the first antenna used for reception or downpath consists of an array of n patches. This array can be used in linear or circular polarization and benefit from two orthogonal polarizations. The second antenna used for transmission or uppath consists of a waveguide terminating in a dielectric rod commonly referred to as a xe2x80x9cpolyrodxe2x80x9d. This antenna can be used in linear or circular polarization and benefit from two orthogonal polarizations. These two antennas are made in such a way that the phase centres of the xe2x80x9cpolyrodxe2x80x9d and of the array of patches practically coincide and can be placed at the focus of the system of antennas.
The aim of the present invention is to incorporate into a transmission/reception source-antenna structure operating in two frequency bands another source-antenna structure which operates in respect of reception, namely the downpath, at a lower working frequency than the other two frequencies, more particularly in a frequency band allowing the reception of conventional satellite television signals. This makes it possible to obtain an antenna structure operating on three frequency bands.
Thus, the subject of the present invention is a source antenna for transmitting/receiving electromagnetic waves comprising means for transmitting electromagnetic waves with longitudinal radiation operating in a first frequency band and means for receiving electromagnetic waves, characterized in that the means for receiving electromagnetic waves consist of a first array of n radiating elements operating in a second frequency band and a second array of nxe2x80x2 radiating elements operating in a third frequency band, the first and second arrays and the longitudinal-radiation means having a substantially common phase centre and the radiating elements of the first and second arrays being arranged around the longitudinal-radiation means.
According to one embodiment, the first array of n radiating elements consists of an array of n patches having linear or circular, orthogonal double polarization, the first array of n patches being connected to a feed circuit made in microstrip technology on a first substrate.
Moreover, the means for transmitting electromagnetic, waves with longitudinal radiation consist of an antenna of the longitudinal-radiation travelling wave type with axis coinciding with the axis of radiation, excited by means comprising a waveguide, the waveguide being filled with a dielectric material. This makes it possible to restrict the dimensions of the cross section of the waveguide and to reduce the guided wavelength inside the guide. Moreover, the antenna of the travelling wave type may consist of a dielectric rod known as a xe2x80x9cpolyrodxe2x80x9d or of a helix.
Furthermore, the second array of nxe2x80x2 radiating elements consists of an array of nxe2x80x2 radiating elements having linear or circular, orthogonal double polarization and a wide band. This array is made, preferably, by using two parallel substrates, one of the substrates being the first substrate receiving the first array.
According to a first embodiment, the substrate is covered with a metallic layer forming an earth plane comprising demetallized zones, at the level of the radiating elements of the second array.
According to a preferred embodiment, the radiating elements of the array with orthogonal double polarization and a wide band consist of two patches which are superimposed and made respectively on each substrate and coupled electromagnetically. In this case, the two substrates may be connected plumb with the demetallized zones by metallic walls.
According to another embodiment, the radiating elements of the array with orthogonal double polarization and with a wide band consist of a patch coupled electromagnetically to. a probe connected to the feed circuit.
According to yet another embodiment, the radiating elements of the array with orthogonal double polarization and a wide band consist of an aperture made in the first substrate and a probe connected to the feed circuit and made on the parallel substrate.
According to yet another embodiment, the radiating elements of the array with orthogonal double polarization and a wide band consist of an aperture made in the first substrate and a patch connected to the feed circuit and made on the parallel substrate.
Moreover, the second array of nxe2x80x2 radiating elements is connected to a feed circuit made in microstrip technology.
According to a characteristic of the present invention, the first array of n radiating elements is an array with four elements arranged in a square and the second array of nxe2x80x2 radiating elements is an array with four elements arranged in a cross around the first array.
In accordance with the present invention, the first and second frequency bands correspond to the Ka band and the third frequency band corresponds to the Ku band.